Semiconductor device and method for fabricating the same

ABSTRACT

A method for fabricating semiconductor device includes the steps of: forming a gate structure on a substrate; forming a polymer block on a corner between the gate structure and the substrate; performing a cleaning process; performing an oxidation process by injecting oxygen gas under 750° C. to form a first seal layer on sidewalls of the gate structure; and forming a source/drain region adjacent to two sides of the gate structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.17/008,633, filed on Aug. 31, 2020, which is a continuation applicationof U.S. patent application Ser. No. 16/503,609, filed on Jul. 4, 2019,all of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method for fabricating semiconductor device,and more particularly to a method of forming polymer block adjacent to agate structure.

2. Description of the Prior Art

With the trend in the industry being towards scaling down the size ofthe metal oxide semiconductor transistors (MOS), three-dimensional ornon-planar transistor technology, such as fin field effect transistortechnology (FinFET) has been developed to replace planar MOStransistors. Since the three-dimensional structure of a FinFET increasesthe overlapping area between the gate and the fin-shaped structure ofthe silicon substrate, the channel region can therefore be moreeffectively controlled. This way, the drain-induced barrier lowering(DIBL) effect and the short channel effect are reduced. The channelregion is also longer for an equivalent gate length, thus the currentbetween the source and the drain is increased. In addition, thethreshold voltage of the FinFET can be controlled by adjusting the workfunction of the gate.

As the semiconductor industry enters 10 nm node generation, theresistance value of metal gates plays an important role in theperformance of the FinFET device. Since metal gate transistorarchitecture today is still insufficient in achieving desirableperformance, how to improve the design of current transistor structurehas become an important task in this field.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a method forfabricating semiconductor device includes the steps of: forming a gatestructure on a substrate; forming a polymer block on a corner betweenthe gate structure and the substrate; performing a cleaning process;performing an oxidation process by injecting oxygen gas under 750° C. toform a first seal layer on sidewalls of the gate structure; and forminga source/drain region adjacent to two sides of the gate structure.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 illustrate a method for fabricating semiconductor deviceaccording to an embodiment of the present invention.

FIG. 6 illustrates a structural view of a semiconductor device accordingto an embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1-5, FIGS. 1-5 illustrate a method for fabricatingsemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 1, a substrate 12 is first provided, inwhich the substrate could be a silicon substrate or silicon-on-insulator(SOI) substrate. A transistor region, such as a PMOS region or a NMOSregion could be defined on the substrate 12. At least a fin-shapedstructure 14 and an insulating layer (not shown) are formed on thesubstrate 12, in which the bottom portion of the fin-shaped structure 14is surrounded by the insulating layer preferably made of dielectricmaterial such as silicon oxide to form a shallow trench isolation (STI)16. It should be noted that even though this embodiment pertains to thefabrication of a non-planar FET device such as FinFET device, it wouldalso be desirable to apply the following process to a planar FET device,which is also within the scope of the present invention.

According to an embodiment of the present invention, the fin-shapedstructure 14 could be obtained by a sidewall image transfer (SIT)process. For instance, a layout pattern is first input into a computersystem and is modified through suitable calculation. The modified layoutis then defined in a mask and further transferred to a layer ofsacrificial layer on a substrate through a photolithographic and anetching process. In this way, several sacrificial layers distributedwith a same spacing and of a same width are formed on a substrate. Eachof the sacrificial layers may be stripe-shaped. Subsequently, adeposition process and an etching process are carried out such thatspacers are formed on the sidewalls of the patterned sacrificial layers.In a next step, sacrificial layers can be removed completely byperforming an etching process. Through the etching process, the patterndefined by the spacers can be transferred into the substrate underneath,and through additional fin cut processes, desirable pattern structures,such as stripe patterned fin-shaped structures could be obtained.

Alternatively, the fin-shaped structure 14 could also be obtained byfirst forming a patterned mask (not shown) on the substrate, 12, andthrough an etching process, the pattern of the patterned mask istransferred to the substrate 12 to form the fin-shaped structure.Moreover, the formation of the fin-shaped structure could also beaccomplished by first forming a patterned hard mask (not shown) on thesubstrate 12, and a semiconductor layer composed of silicon germanium isgrown from the substrate 12 through exposed patterned hard mask viaselective epitaxial growth process to form the corresponding fin-shapedstructure. These approaches for forming fin-shaped structure are allwithin the scope of the present invention.

Next, at least a gate structure 18 or dummy gate is formed on thesubstrate 12. In this embodiment, the formation of the gate structure 18could be accomplished by a gate first process, a high-k first approachfrom gate last process, or a high-k last approach from gate lastprocess. Since this embodiment pertains to a high-k last approach, agate dielectric layer or interfacial layer 20, a gate material layer 22preferably made of polysilicon, a hard mask 24, and another hard mask 26could be formed sequentially on the substrate 12, and a pattern transferprocess is then conducted by using a patterned resist (not shown) asmask to remove part of the hard masks 26, 24, part of the gate materiallayer 22 and part of the gate dielectric layer through single ormultiple etching processes. After stripping the patterned resist, a gatestructure 18 composed of an un-patterned interfacial layer 20, apatterned gate material layer 22 or gate electrode layer, and patternedhard masks 24, 26 are formed on the substrate 12. In this embodiment,the interfacial layer 20 is preferably made of silicon oxide, the hardmask 24 is made of silicon nitride, and the hard mask 26 is made ofsilicon oxide.

It should be noted that hydrogen bromide (HBr) and/or nitrogen gas arepreferably used as etching gas during the aforementioned patterningprocess to sequentially remove part of the hard masks 26, 24 and part ofthe gate material layer 22 for forming the gate structure 18.Preferably, at least a polymer block 28 or fin corner oxide (FCO) isformed during the etching process on sidewalls of the gate structure 18or more specifically on a corner or corners between sidewalls of thegate structure 18 and top surface of the substrate 12 (or interfaciallayer 20). In this embodiment, the composition of the polymer block 28or FCO could vary depending on the content of the gas used during theaforementioned etching process including but not limited to for examplefluorine (F), bromide (Br), and/or silicon (Si). It should also be notedthat even though polymer bocks 28 are formed on corners betweensidewalls of the gate structure 18 and the substrate 12 in thisembodiment, according to another embodiment of the present invention, itwould also be desirable to form polymer block 18 only between onesidewall of the gate structure 18 and the top surface of the substrate12, such as on the corner between left sidewall of the gate structure 18and top surface of the substrate 12 (or interfacial layer 20) or on thecorner between right sidewall of the gate structure 18 and top surfaceof the substrate 12 (or interfacial layer 20), which are all within thescope of the present invention. Moreover, it would also be desirable toconduct an optional cleaning process for removing residues on thesurface of the substrate 12 after the formation of the gate structure18. Nevertheless, it should be noted that whether the cleaning processis conducted or not polymer blocks 28 are preferably formed on thecorner (or corners) between sidewalls of the gate structure 18 and topsurface of the substrate 12 (or interfacial layer 20) after the gatestructure 18 is formed.

Next, as shown in FIG. 2, a re-oxidation process is conducted to form afirst seal layer 30 on sidewalls of the gate structure 18. Specifically,the re-oxidation process conducted at this stage is accomplished byusing furnace or dry etching approach to inject oxygen gas underapproximately 750° C. to form a first seal layer 30 made of siliconoxide on top surface and sidewalls of the gate structure 18, includingsidewalls of the gate material layer 22, sidewalls of the hard mask 24,and sidewalls and top surface of the hard mask 26. It should be notedthat the oxygen gas applied throughout the re-oxidation processpreferably penetrates or diffuses through the polymer blocks 28 tooxidize all of the sidewalls of the gate structure 18. In other words,the first seal layer 30 is preferably formed on the inner sidewalls ofthe polymer blocks 28 or if viewed from another perspective, the innersidewalls of the first seal layer 30 preferably contact the gatestructure 18 directly while the outer sidewalls of the first seal layer30 contacts the inner sidewalls of the polymer blocks 28 directly.

Next, as shown in FIG. 3, a second seal layer 32 is formed on sidewallsof the first seal layer 30 and the polymer blocks 28, and an etchingback process is conducted to remove part of the second seal layer 32 andpart of the first seal layer 30 to form a first spacer 34 and a secondspacer 36 on sidewalls of the gate structure 18. In this embodiment, thefirst spacer 34 and the second spacer 36 are preferably made ofdifferent materials, in which the first spacer 34 is preferably made ofsilicon oxide while the second spacer 36 is made of siliconoxycarbonitride (SiOCN). Nevertheless, according to other embodiments ofthe present invention, the second spacer 36 could also be selected fromthe group consisting of silicon oxide, silicon nitride (SiN), siliconoxynitride (SiON), and silicon carbon nitride (SiCN).

Next, a dry etching and/or wet etching process is conducted by using thegate structure 18 and second spacer 36 as mask to remove part of thesubstrate 12 along the second spacer 36 to form a recess (not shown)adjacent to two sides of the gate structure 18.

Next, a selective epitaxial growth (SEG) process is conducted to form anepitaxial layer 38 in the recess. In this embodiment, a top surface ofthe epitaxial layer 38 is preferably even with a top surface of thesubstrate 12, in which the epitaxial layer 38 also shares substantiallysame cross-section shape with the recess. For instance, thecross-section of the epitaxial layer 38 could also a circle, a hexagon,or an octagon depending on the demand of the product. In thisembodiment, the epitaxial layer 38 could also be formed to includedifferent material depending on the type of transistor being fabricated.For instance, if the MOS transistor being fabricated were to be a PMOStransistor, the epitaxial layer 38 could be made of material includingbut not limited to for example SiGe, SiGeB, or SiGeSn. If the MOStransistor being fabricated were to be a NMOS transistor, the epitaxiallayer 38 could be made of material including but not limited to forexample SiC, SiCP, or SiP. Moreover, the SEG process could also beadjusted to form a single-layered epitaxial structure or multi-layeredepitaxial structure, in which heteroatom such as germanium atom orcarbon atom of the structure could be formed to have gradient while thesurface of the epitaxial layer 38 is preferred to have less or nogermanium atom at all to facilitate the formation of silicideafterwards. It should be noted that even though the top surfaces of thesubstrate 12 and epitaxial layer 38 are coplanar in this embodiment, itwould also be desirable extend the epitaxial layer 38 upward so that thetop surface of the epitaxial layer 38 is higher than the top surface ofthe substrate 12 according to another embodiment of the presentinvention.

Next, an ion implantation process is conducted to form a source/drainregion 40 in part or the entire epitaxial layer 38. According to anembodiment of the present invention, the source/drain region 40 couldalso be formed insituly during the SEG process. For instance, thesource/drain region 40 could be formed by implanting p-type dopantsduring formation of a SiGe epitaxial layer, a SiGeB epitaxial layer, ora SiGeSn epitaxial layer for PMOS transistor, or could be formed byimplanting n-type dopants during formation of a SiC epitaxial layer,SiCP epitaxial layer, or SiP epitaxial layer for NMOS transistor. Bydoing so, it would be desirable to eliminate the need for conducting anextra ion implantation process for forming the source/drain region.Moreover, the dopants within the source/drain region 40 could also beformed with a gradient, which is also within the scope of the presentinvention.

Next, as shown in FIG. 4, a contact etch stop layer (CESL) 42 is formedon the substrate 12 surface and the gate structure 18, and an interlayerdielectric (ILD) layer 44 is formed on the CESL 42 afterwards. Next, aplanarizing process such as a chemical mechanical polishing (CMP)process is conducted to remove part of the ILD layer 44 and part of theCESL 42 to expose the hard mask 26 so that the top surfaces of the hardmask 26 and ILD layer 44 are coplanar. In this embodiment, the CESL 42could include silicon nitride while the ILD layer 44 could includesilicon oxide, but not limited thereto.

Next, as shown in FIG. 5, a replacement metal gate (RMG) process isconducted to transform the gate structure 18 into a metal gate 46. Forinstance, the RMG process could be accomplished by first performing aselective dry etching or wet etching process using etchants includingbut not limited to for example ammonium hydroxide (NH₄OH) ortetramethylammonium hydroxide (TMAH) to remove the hard masks 24, 26 andgate material layer 22 for forming a recess (not shown) in the ILD layer44. Next, a high-k dielectric layer 48, a work function metal layer 50,and a low resistance metal layer 52 are formed in the recess, and aplanarizing process such as CMP is conducted to remove part of lowresistance metal layer 52, part of work function metal layer 50, andpart of high-k dielectric layer 48 to form metal gate 46. In thisembodiment, the gate structure or metal gate 46 fabricated throughhigh-k last process of a gate last process preferably includes aninterfacial layer 20 or gate dielectric layer, a U-shaped high-kdielectric layer 48, a U-shaped work function metal layer 50, and a lowresistance metal layer 52. Next, part of the low resistance metal layer52, part of the work function metal layer 50, and part of the high-kdielectric layer 48 are removed to form a recess, a hard mask 54 isformed in the recess, and a planarizing process such as CMP is conductedto remove part of the hard mask 54 so that the top surfaces of the hardmask 54 and ILD layer 44 are coplanar.

In this embodiment, the high-k dielectric layer 48 is preferablyselected from dielectric materials having dielectric constant (k value)larger than 4. For instance, the high-k dielectric layer 48 may beselected from hafnium oxide (HfO₂), hafnium silicon oxide (HfSiO₄),hafnium silicon oxynitride (HfSiON), aluminum oxide (Al₂O₃), lanthanumoxide (La₂O₃), tantalum oxide (Ta₂O₅), yttrium oxide (Y₂O₃), zirconiumoxide (ZrO₂), strontium titanate oxide (SrTiO₃), zirconium silicon oxide(ZrSiO₄), hafnium zirconium oxide (HfZrO₄), strontium bismuth tantalate(SrBi₂Ta₂O₉, SBT), lead zirconate titanate (PbZr_(x)Ti_(1-x)O₃, PZT),barium strontium titanate (Ba_(x)Sr_(1-x)TiO₃, BST) or a combinationthereof.

In this embodiment, the work function metal layer 50 is formed fortuning the work function of the metal gate in accordance with theconductivity of the device. For an NMOS transistor, the work functionmetal layer 50 having a work function ranging between 3.9 eV and 4.3 eVmay include titanium aluminide (TiAl), zirconium aluminide (ZrAl),tungsten aluminide (WAl), tantalum aluminide (TaAl), hafnium aluminide(HfAl), or titanium aluminum carbide (TiAlC), but it is not limitedthereto. For a PMOS transistor, the work function metal layer 50 havinga work function ranging between 4.8 eV and 5.2 eV may include titaniumnitride (TiN), tantalum nitride (TaN), tantalum carbide (TaC), but it isnot limited thereto. An optional barrier layer (not shown) could beformed between the work function metal layer 50 and the low resistancemetal layer 52, in which the material of the barrier layer may includetitanium (Ti), titanium nitride (TiN), tantalum (Ta) or tantalum nitride(TaN). Furthermore, the material of the low-resistance metal layer 52may include copper (Cu), aluminum (Al), titanium aluminum (TiAl), cobalttungsten phosphide (CoWP) or any combination thereof. Next, a contactplug formation could be conducted by forming contact plugs 56 in the ILDlayer 44 and CESL 42 to electrically connect the source/drain region 40adjacent to two sides of the second spacer 36. This completes thefabrication of a semiconductor device according to an embodiment of thepresent invention.

Referring again to FIG. 5, which further illustrates a structural viewof a semiconductor device according to an embodiment of the presentinvention. As shown in FIG. 5, the semiconductor device preferablyincludes a gate structure 18 disposed on the substrate 12, a firstspacer 34 disposed on sidewalls of the gate structure 18, a secondspacer 36 disposed on sidewalls of the first spacer 34, polymer blocks28 disposed between the first spacer 34 and the second spacer 36 andalso on corners between the gate structure 18 and the substrate 12, anda source/drain region 40 adjacent to two sides of the gate structure 18.

Overall, each of the polymer blocks 28 is surrounded by the first spacer34, the interfacial layer 20, and the second spacer 36. It should benoted that even though each of the polymer blocks 28 includes atriangular cross-section in this embodiment, according to otherembodiment of the present invention, the shape of polymer blocks 28could also vary depending on the gas used during the aforementionedetching process. For instance, each of the polymer blocks 28 couldinclude circular, rectangular square, or other irregular shapes.Preferably, the overall height of each of the polymer blocks 28 is lessthan 1/10 or even 1/20 of the entire height of the gate structure 18.

In this embodiment, the first spacer 34 and the polymer blocks 28 arepreferably made of different materials and the second spacer 36 and thepolymer blocks 28 are made of different materials, in which the firstspacer 34 preferably includes silicon oxide, the second spacer 36includes SiOCN, and the composition of the polymer block 28 could varydepending on the content of the gas used during the aforementionedetching process. According to an embodiment of the present invention,the polymer block 28 could include elements including but not limited tofor example fluorine (F), bromide (Br), and/or silicon (Si).

Referring to FIG. 6, FIG. 6 illustrates a structural view of asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 6, in contrast to not removing any of theinterfacial layer 20 on the surface of the substrate 12 while usingetching process to remove part of the hard masks 24, 26, and the gatematerial layer 22, it would also be desirable to remove a part of theinterfacial layer 20 as the hard masks 24, 26 and the gate materiallayer 22 are patterned to form gate structure 18 so that no interfaciallayer 20 remains on the surface of the fin-shaped structure 14 adjacentto two sides of the gate structure 18. Next, processes in FIGS. 2-5 areconducted to form polymer blocks 28, first spacer 34, and second spacer36 on sidewalls of the gate structure 18, form a CESL 42 and ILD layer44 on the gate structure 18, and performing a RMG process to transformpolysilicon gate structure 18 into metal gate 46. Structurally, since nointerfacial layer 20 remains on the surface of the substrate 12 adjacentto two sides of the gate structure 18 or directly under the polymerblocks 28 so that the polymer blocks 28 contact the substrate 12directly, each of the polymer blocks 28 is surrounded by the firstspacer 34, the substrate 12, and the second spacer 36 instead of beingsurrounded by the first spacer 34, the interfacial layer 20, and thesecond spacer 36 in the aforementioned embodiment.

In current FinFET process, polymer blocks or fin corner oxide (FCO)residues are often formed on corners between gate structure and thesubstrate during formation of the gate structure, and the polymer blocksare then sealed between gate electrode and the spacer formed afterwards.Since the polymer blocks in current process are typically sealedimmediately adjacent to or directly contacting the gate material layeror gate electrode made of polysilicon, the polymer blocks are oftenremoved along with the polysilicon gate material layer during the RMGprocess and results in severe leakage. To resolve this issue, thepresent invention preferably conducts an oxidation process to form afirst seal layer 30 or first spacer 34 between sidewalls of the gatestructure and inner sidewall of the polymer block after the polymerblocks are formed on corners between gate structure and the substrate.By using the first spacer 34 as a barrier structure between the polymerblocks and the gate structure, it would be desirable to prevent leakagewhen gate material layer made of polysilicon is removed during RMGprocess.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for fabricating semiconductor device,comprising: forming a gate structure on a substrate; forming a polymerblock on a corner between the gate structure and the substrate;performing a cleaning process; performing an oxidation process byinjecting oxygen gas under 750° C. to form a first seal layer onsidewalls of the gate structure; and forming a source/drain regionadjacent to two sides of the gate structure.
 2. The method of claim 1,further comprising forming the polymer block on a corner betweensidewalls of the gate structure a top surface of the substrate.
 3. Themethod of claim 1, further comprising performing the oxidation processto oxidize sidewalls of the gate structure to form the first seal layer.4. The method of claim 1, further comprising forming the first seallayer on sidewalls of the gate structure and an inner sidewall of thepolymer block.
 5. The method of claim 1, further comprising: forming agate material layer on the substrate; forming a first hard mask on thegate material layer; forming a second hard mask on the first hard mask;and patterning the second hard mask, the first hard mask, and the gatematerial layer to form the gate structure and forming the polymer block.6. The method of claim 1, further comprising: forming a second seallayer on sidewalls of the first seal layer and the polymer block;removing the second seal layer and the first seal layer to form a firstspacer and a second spacer; forming the source/drain region adjacent totwo sides of the second spacer; forming an interlayer-dielectric (ILD)layer on the gate structure; and performing a replacement metal gate(RMG) process to transform the gate structure into a metal gate.
 7. Themethod of claim 6, wherein sidewalls of the polymer block contact thefirst spacer and the second spacer.
 8. The method of claim 1, whereinthe polymer block comprises silicon.